[2.13] Boosting the Star Formation Rate by Minor Tidal Interactions

For a statistical sample of late type spiral galaxies (Sab
to Sbc), we explore whether the global star formation rate
(SFR) over the last 0.5~Gyrs is correlated with
indicators of recent weak tidal interactions. We obtain
integrated spectra (3500Å-5300Å) of our sample
galaxies and study the stellar populations and emission line
characteristics as a function of the lopsidedness \langle
A1/A0 \rangle\phi,r. We quantify the recent SF
history of our galaxies by comparing the relative abundance
of A stars (via the strength of Balmer absorption),
and the abundance of massive stars (via the EW of (H
\beta) emission), between symmetric and losided galaxies of
the same Hubble type. We find that the recent SFR of a
galaxy is correlated to its lopsidedness. Significant
lopsidedness is most likely caused by minor tidal
interactions and is found in over 20% of the disk galaxy
population (Rudnick and Rix, 1998.) Coupled with the short
lifetime of lopsided structures, this implies that the
average disk galaxy has undergone multiple periods of
boosted SFR caused by weak interactions.